My recent experience:
This took place in Upstate NY, not Canada, but it might be relevant to your decision making.
We bought land and subdivided with my brother-in-law. Both of us built temporary buildings before the final building. We were like you in not knowing how to avoid legal trouble. Luckily, and I think this applies everywhere, a two minute discussion at the local town hall told us everything we needed to know. This started a non-combative relationship with code enforcement.
Our local code required a permit and inspection for any structure over 100 sq ft. My brother-in-law avoided that by keeping his shack under that size. No permit, no inspection, no required footers, insulation, nada. The county still came out to visually inspect (looking for a way to increase tax base I expect) but that's it. He seems happy with that decision. My viewpoint was that he made a questionable decision. He is always crushed for space, has had to spend the money to make a couple other outbuildings, and is never really comfortable.
We went ahead and built a 20x24 building. This required a permit ($25), a "during" inspection (made sure footers where deep enough- no cost), and final inspection (make sure it would not fall on our heads-no cost). Our value of our property also got bumped up by $2,500 which added about $15 to our annual taxes.
So very little extra cost for a much more comfortable space. Plus the inspector gave us good advice along the way. And when we built our final house, he already knew us and was on our side. He let a few (non important but technically required) things slide and gave more good, money saving advice. Actually, he helped me save thousands now that I think of it. He knew some local sources for materials, and some techniques that saved me some additional work.
No regrets for either my brother-in-law or us actually. But there's something to consider. Our temporary building is now an combo outbuilding, canning shed, and art studio - and of course a hefty mess in the loft.